Men who have sex with men (MSM) are highly impacted by HIV in the U.S. Marked disparities by race/ethnicity exist in HIV infection rates and engagement and retention in care along the HIV care continuum. Higher HIV acquisition rates among Black MSM are not fully explained by individual-level risk behaviors, while lower engagement and retention in care are exacerbated by factors that extend beyond the individual. In order to develop comprehensive, multi-level interventions to improve completion of steps along the HIV care continuum for Black and White MSM, it is critical to understand the mechanisms in which neighborhoods and social and sexual networks influence retention in care, antiretroviral therapy (ART) adherence, and viral suppression, and ascertain how these pathways differ by race/ethnicity. Using a socioecological theoretical framework, we propose to identify neighborhood-and network-level characteristics associated with HIV care outcomes among Black, non-Hispanic and White, non-Hispanic HIVinfected MSM in New York City (NYC) in a longitudinal study. We will focus on 3 potential neighborhoods of influence: home, social, and health facility access neighborhoods. We will investigate the influence of 4 neighborhood-level characteristic domains: (1) community violence, physical disorder, and social disorganization; (2) neighborhood alcohol and other drug (AOD) use-associated factors; (3) neighborhood-level social norms; (4) community resources. In this proposal, we will explore the following Specific Aims: Aim 1: To use spatial analysis to characterize clustering and spatial trends in HIV care outcomes (retention in care, ART adherence, and viral suppression) among Black and White HIV-infected MSM in NYC. Aim 2: To examine HIV care outcomes by race/ethnicity among Black and White HIV-infected MSM in NYC in relationship to longitudinal changes in: 2A. Exposure to neighborhoods of potential influence (home, social, health facility access). 2B. Neighborhood characteristics in four conceptual domains (community violence/physical disorder/social disorganization, neighborhood AOD use-associated factors, neighborhood-level social norms, community resources). 2C. Social and sexual networks. Aim 3: To use multilevel modeling to assess associations among changes over time in exposure to the 4 neighborhood characteristic domains and changes in social and sexual networks with HIV care outcomes by race/ethnicity, while assessing the potential mediating effects of individual- and network-level factors. The study will employ an innovative approach combining geospatial mapping of neighborhoods with methods from the field of spatial statistics and an existing, extensive geospatial database. The study will have direct implications for the design of neighborhood- and network-level interventions to improve the HIV care continuum for MSM, particularly for Black MSM.